Testing perception of space



Aug 8, 1939. AMEs' JR 2,168,308

TESTING PERCEPTION OF SPACE Filed Sept. 24, 1935 10 Sheets-Sheet l W 11:9

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TESTING PERCEPTION OF SPACE 1O Sheets-Sheet 3 Filed Sept. 24, 1955 07ml? flmes Jr @W m Aug. 8, 1939.

A. AMES, JR 2,168,308

TESTING PERCEPTION OF SPACE Filed Sept. 24, 1935 10 Sheets-Sheet 4 8, 1939 A. AMES, JR 2,168,368

TESTING PERCEPTION OF SPACE Filed Sept. 24, 1955 lo Sheets-Sheet 5 727306758 07 fia'eaeri $77365 Jr:

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TE F'ING PERCEPTION OF SPACE Filed Sept. 24, 1935 10 Sheets-Sheet 5 Izaak/ 7250? flai'gller? Vina; J.

Aug. 8, 1939.

A. AMES, JR

TESTING PERCEPTION OF SPACE Filed Sept. 24, 1935 10 Sheets-Sheet 7 Aug. 8, 1939. A. AMES, JR 2,168,308

TESTING PERCEPTION OF SPACE Filed Sept. 24, 1955 10 Sheets-Sheet $3 KAN R Aug. 8, 1939.

A. AMES, JR

TESTING PERCEPTION OF SPACE Filed Sept. 24, 1935 10 Sheets-Sheet 9 wwN wig 5 A. AMES, vJR

Aug. 8, 1939.

TESTING PERCEPTION OF SPACE l0 SheetsSheet 10 Filed Sept. 24, 1935 Patented Aug. 8, 1939 2 UNITED STATES PATENT OFFIQE TESTING PERCEPTION F SPACE Adelbert Ames, Jr., Hanover, N. H., assignor to Trustees of Dartmouth College, Hanover, N. H., a corporation of New Hampshire Application September 24, 1935, Serial No. 41,890

23 Claims. (01. 88-20) The present invention deals with the problem Fig. 21 is a side elevation, partly in section, of of testing human eyes, especially with regard to another embodiment of my invention; space perception. Fig. 22 is a front elevation of the embodiment Some of the principal objects of the invention shown in Fig. 21;

are to provide methods, and means for carrying Fig. 23 is a section on line 2323 of Fig. 21; 5

out such methods, for determining correct per- Fig. 24 is a section on line 24 24 of Fig. 21; ception of space as dependent on orientation, and g- 5 s a Se tion O l e 2525 Of monocular and binocular vision, to check the 26 is Similar t but With a p p presence or absence of correct space perception, e f a se e a d With a e holder p;

and to determine or to check correcting instru- 7 a sc e t a w g of the p p cl0 mentalities suitable to restore correct perception Give Object of of space, especially as influenced by the relative g. 28 is a section on line 28-28 of Fig. 2 size or shape, of the ocular images. Fig. 29 is a front elevation of the lens holder These and other objects, aspects and features of ShOWn in and my invention will be apparent from the following Figsto 39 are diagrams d a g the 15 detailed explanation illustrating the genus of the esponse of the new testing method to certain invention with reference to several embodiments Ocular defectsthereof, Th description refers t drawings in The position of objects relatively to one another, which: and to a system of reference including the ob- 20 Figs. 1,2and3are diagrams explaining bin server himself is made conscious to the latter lar vision in its relation to the present invention; thlfiugh the influence of V ou factors. On the Figs. 4 and 5 are schematical representations of one hand, his Orientation in Space ath r n t principle of t pyesent invention, including the gravitational field constituting a system of possible arrangements f carrying out my new reference),is conveyed to him mainly through the 23 test and its relation to the eyes to be tested, in function of his static sense or his vestibular balisometric projection and vertical section, respecance apparatus both, including the vestibule tively, and the semicircular canals in the bony labyrinth Fig. 6 is a diagram explaining the adaptation of the internal i type of space perciption 0 a test screen to the fusional area; glrll be referied to herein as vestibular orienta- Figs. '7 and 8 are sections through test screens On'the other hand the position of Objects rela as indicated in Fig. 6; Figs. 9 and 10 show, in schematical plan View 53 2 ggf i gg g 3 3 22 g zifigg and side elevation, respectively, a device for Warpmanly through his Contact with the objects by i i g 33 F22 t 9 bemg palty a sectlon on visual response, other contacts as touch, hearing, 55 temperature and others being of secondary imt 2% P i g g ii g z 5 portance. Visual response again, as inducing es g evfce g an par y m perception of the location of objects in space, opersection on line I i-i i of Fig. 12; ates in Various Ways m Fig. 12 1s a vertical section on line |2|2 of one Way of Visual space perception is primarily 4U a n based on the fact that ocular images are of the 10 IS a Vertlcal Section on 11118 of nature of conical projections or perspectives with F1312, their Well-known diiferent representation of ob- F 14 is a v t al sectlon 0n hne 0f jects differently located in space, although otherwise of similar characteristics. Phenomena of Fig. 15 is a section on line [5-45 of Fig. 14; Fig. 16 is a front elevation of an embodiment with vertical test planes;

similar effect are those due to aerial perspective (that is, color changes due to distance), to the peculiar structure of the human eye (as, for ex- Fig. 17 is a vertical section on line |'l-l'l of amme producing difi ent 0010f fring at 1; F ferent distances, or changing the sharpness of 50 Fig. 18 is a plan of an object for testing near contours with their distances), to the eifect of vision; obstruction of distant objects by nearer ones, to Fig. 19 is a section on line lS-IQ of Fig. 18; parallax resulting from movement of the eyes, Fig. 20 is a View of a test frame to be used with and others. the device according to Figs. 18 and 19; This type of space perception is, of course, effe 55 tive in purely monocular vision, although, as will be presently discussed, perspective is also a factor in binocular vision. Space perception through perspective, conveyed to consciousness only by one eye, will be referred to herein as monocularly perspective vision.

Another way of becoming cognizant of the distribution of objects and surfaces in space is through stereoscopic vision. Due to the lateral separation of the two eyes of an individual, a field including objects at different distances produces diiferent ocular images. The slight disparities of the positioning of the two images of the same objects tells the observer the relative distance of the objects. In stereoscopic vision, two causes of ocular image disparity can be distinguished.

One cause is the dissimilarity of the perspectives in the two eyes, these different perspective appearances being mentally interpreted into three dimensions. This type of space perception will be termed perspective stereoscopic vision.

Another cause of stereoscopic vision is disparity of the ocular images due to causes other than perspective, it being evident that objects which lend themselves poorly, or not at all, to inducing perspective (for example, objects not having rectilinear patterns) nevertheless can be located in space if binocularly seen. This phase of space perception will herein be called non-perspective stereoscopic vision.

In this context, the term ocular image is used to describe the impression formed in the higher brain centers through the vision of one eye. It is determined not only by the properties of the dioptric image that is formed on the retina of the eye, but also by the modifications imposed upon that image by the anatomical properties and physiological processes by which this optical image is carried to the higher brain centers. Visual conditions which have to do with the size and shape of ocular images are shortly termed eikonic, the condition in which the size or shape, or both, of ocular images are incongruent' is referred to an aniseikonia, and the condition where the ocular images are substantially congruent, as iseikonia.

Aniseikonia includes overall ocular image size differences in which one image is larger than the other in all meridians, and meridional differences in which one image is larger than the other in one meridian. This term also includes incongruence in binocular vision introduced by anomalies of the declinations of the eyes. This declination aniseikonia is characterized by relative rotation of certain meridians of the ocular images.

Different declinations of corresponding meridians of the ocular images are an actually observed defect which can be artificially produced by obliquely applied meridional size or eikonic lenses, that is lenses changing the image size in one meridian without affecting the light vergence, as for example described in Patent No. 1,933,578, of November '7, 1933. Referring to Fig. 1, if a rectangular cross N is observed through such a lens, the images X, Y, of meridians X and Y will form an angle different from angle subtended by meridians X and Y,

A cause of this defect may be deformation of the eyeball, or certain aspects of the muscular defect known as cyclophoria. If the upper ends of the vertical diameters of the ocular images are tipped nasalward, the error of declination is called conclination, while, if the upper ends, are tipped templeward, the error of declination is termed disclination.

It has been observed that it does not matter with regard to binocular space perception Whether or not horizontal meridians are turned relatively to one another. The relative rotation of horizontal meridians influences binocular vision to a substantial degree only when it becomes so pro nounced that it interferes with or actually breaks fusion, that is, makes binocular vision difficult or impossible.

Still another type of aniseikonia is asymmetric distortion similar to the effect of prismatic lenses, as for example described in copending application Serial No. 750,162, filed November 26, 1934.

The concept of vestibular orientation needs no further explanation, but a few facts concerning monocularly perspective vision and stereoscopic vision (non-perspective as well as perspective) will have to be given in order to facilitate the understanding of the present invention.

An object viewed monocularly appears at different distances if the overall size of the respective ocular image is changed, the object appearing more distant if the image becomes smaller, and vice versa, these changes being, however, not very pronounced and in most cases negligible since the aniseikonic differences connected with binocular vision are only a few percent. Changes in the horizontal meridian, and likewise in the vertical meridian have no substantial effect upon the apparent distance of monocularly seen objects. The above explained declination aniseikonia causes vertical lines to appear tipped, but this effect is only of secondary character regarding judgment of position of monocularly seen objects in space. As a whole, it can be said that monocularly perspective vision is not substantially influenced by changes in size or shape of ocular images.

Coming now to stereoscopic vision, its nonperspective aspect will first be discussed with reference to Fig. 2. In this figure, I and II are two objects in space at different distances from the observer whose right and left eyes are shown at R and L, respectively. If the observer fixes object I, images of I are formed on the fovea of each eye at FE and FL. Images of point II are formed on the retina at HR and IIL, respectively. It is evident that the similar images HR, and IIL are formed at disparate points of the retina, at different sides of points IIIR and IIIL which would correspond to a point III which lies on the horopter passing through point I. This disparity is translated into difference in distance and object II appears as a single object farther away than object I. It will be easily seen that an analogous disparity exists for an object nearer than I. The particular nature and amount of this disparity is translated into difference in distance. The normal threshold sensitivity for this disparity is very low, an angle of about 10", so that stereoscopic judgment of depth is very accurate.

The effect of aniseikonia upon non-perspective stereoscopic space perception will now be understood to take place as follows:

In Fig. 2, the distance that object II is seen behind I depends upon the particular disparity of images HR and IIL from points IIIR and IIIL. If for some reason the relation of size or shape, or both, of the ocular images is changed, for example the image of the right eye as compared with that of the left, this particular disparity is changed and II appears nearer if the right ocular image is smaller, or farther if the latter is larger. The magnitude of these changes is relatively great, increasing with distance. For example, a difference of 3% in the horizontal meridian of the two ocular images causes a surface at the distance of one meter to appear tipped about 19.

The above applies strictly only to objects perceived substantially without the influence of perspective, that is, to non-perspective stereoscopic vision. If the binocularly viewed object is one in which there is perspective, apparent changes due to that perspective also result from aniseikonia but they are very much less in degree, so that they can be neglected in many instances. Moreover, these minor apparent changes induced in perspective objects by aniseikonia, especially when the perspective objects are three dimensional, may be inconsistent. This can be explained by referring to Fig. 3 which shows a three dimensional object giving marked perspective stereoscopic vision. This object is a box it held near to the eyes, of a length approximately equal to the distance between the pupils of the eyes which are looking into the box, the normal ocular image being indicated at L and OR. Nith this particular arrangement each eye sees in perspective a part of the object which is not seen in perspective by the other eye, namely, the respective side walls SL and SR of the box. The image of one eye, for example the left eye, may now be changed in the horizontal meridian, for example, by means of a no power size lens SL, indicated in dotted lines. Since the parallelism of the edges of the top and bottom and sides of the box and of the front edges of the box are not affected by the size lens these portions will appear parallel and perpendicular to the base line of the eyes. But it is evident that to the left eye with the larger ocular image the back and the front edges of the box will appear longer than they will to the right eye, and that the right-hand side of the box SR will subtend a greater angle to the left eye than the left-hand side OR will to the right eye. As a result, the right-hand side of the box will be interpreted as being nearer than the lefthand side, in which case the box will appear to be tipped as if the right-hand side was nearer than the left, which is inconsistent with the parallelism of the edges of the box. Moreover, the right-hand side of the box appears deeper than the left-hand side. Due to these conditions, if judged from the front edge of the box the back of the box will appear to be tipped as if its right-hand side was further away than its left-hand side; or if judged from the back of the box, the righthand front edge of the box may appear as though nearer than the left-hand front edge. In other words, the difference in size and shape of the ocular images produces an inconsistent interpretation from the point of view of perspective stereoscopic vision. However, this false interpretation is of a relatively small amount compared with the interpretation produced in non-perspective stereoscopic vision by the same aniseikonic difference. Moreover, perspective stereoscopic vision only exists for near objects where the difference of the point of View of the two laterally separated eyes is marked. It decreases with distance and is entirely negligible beyond a hundred or two hundred feet. The effect of aniseikonia on nonperspective stereoscopic vision not only takes place at all distances, but becomes more marked with greater distances.

In general, where there are perspective features in the field of view they are relied upon by the observer to tell him the position of the objects in the field of view. As such perspective features are only affected in a second or third order by aniseikonic differences, such defects do not have a marked effect on the judgment of interpretation of objective space where there are perspective patterns in the field of View. Moreover, it is possible according to the present invention, to separate the effects of perspective and non-perspective stereoscopic vision, as will be discussed hereinafter.

In order to assure correct perception of the distribution of objects in space (assuming that visual acuity of both eyes is satisfactory), monocularly perspective vision should be as perfect as possible, and normal disparateness of binocular vision should be correct through proper congruence of the ocular images of the two eyes. For normal vision giving optimum correctness of space perception the apparent positions of objects as derived from all factors involved, especially from vestibular orientation, monocular perspective vision, perspective stereoscopic vision and non-perspective stereoscopic vision should substantially conform to one another.

Based on these considerations I determine, according to the present invention, on the one hand the judgment of spatial relations generally as dependent on the relative quality of vestibular orientation and monocular and binocular (perspective as well as non-perspective) vision of a person, and, on the other hand, the conditions of the various types of visual space perception by comparing the actual location of objects with the apparent location thereof as derived from vestibular orientation, monocularly perspective vision, perspective stereoscopic vision and non-perspective stereoscopic vision. According to my invention, I also determine defects of binocular vision 01' monocular vision by such comparisons of the apparent and the actual positions of objects in space. Assumin vestibular orientation to be substantially correct (it will be shown hereinafter in which manner the correctness of vestibular orientation can be checked according to my invention), and since monocular vision can be corrected with conventional means and then assumed to be substantially perfect, this determination will be di rected mainly towards the evaluation of defects of binocular vision.

Since, further, perspective stereoscopic vision is either independent of aniseikonia or can be disassociated therefrom as mentioned above, the comparison of the various kinds of space perception results principally in the evaluation of nonperspective stereoscopic vision as affected by aniseikonia or disparity of ocular images.

According to one aspect of my invention, I determine defects of non-perspective stereoscopic vision, which are mainly due to aniseikonia, by comparing non-perspective stereoscopic vision with any one, or combinations of, space perception derived from vestibular orientation, from monocularly perspective vision, or from binocular perspective vision.

Heretofore, the normality of foveal stereoscopic vision has been investigated by the methods well known for that purpose, and peripheral stereoscopic vision in the horizontal meridian with so-called horopter tests. However, in the latter tests the standard against which the hempter is set is an imaginary plane or surface, the uncertainty of the position of such a standard surface making these tests frequently not very exact. Also, such tests take into consideration only certain horizontal meridians, whereas my' new testing method is not confined to any particular meridian, plane, object pattern or visual distance.

In another aspect of the invention, it is possible to find optical means for correcting defects of binocular vision by either changing trial corrections until binocular vision agrees with essentially correct space perception derived from other sources, or by deriving the necessary amount of binocular correction from the apparent deviation of objects, on the one hand as seen with nonperspective stereoscopic vision, and, on the other hand, as perceived in space by diiierent types of space perception which latter may be assumed to be correct.

Still other objects of my invention are to provide methods for presenting to a pair of eyes objects inducing non-perspective stereoscopic space perception in a manner permitting comparison of that perception with the faculty of vestibular orientation; to present for comparison to a pair of eyes objects that induce principally only space perception due to the characteristics of non-perspective stereoscopic vision and to one eye of the pair objects especially conductive to induce space perception due to monocular perspective; to provide methods for presenting for comparison to a pair of eyes objects inducing non-perspective stereoscopic vision, and objects inducing space perception due to perspective stereoscopic vision; to provide a method for detecting and determining defects of binocular vision by comparing the apparently correct posit ons of objects seen principally with perspective and non-perspective stereoscopic space perception, respectively; to provide means for presenting to a person objects which are seen by one eye or by both eyes with the characteristics determining space perception through perspective, and by both eyes with the characteristics principally inducing non-perspective stereoscopic space perception; to provide apparatus permitting comparison and determination of the relative location of an object inducing mainly perspective space perception with an object inducing mainly non-perspective stereoscopic space perception; to provide methods and means for carrying out such methods for comparing space perception due to the orientation faculty, monocular perspective, perspective and non-perspective stereoscopic vision for difierent visual distances and planes; to provide means, either optical or mechanical, for changing the relative positions in space of objects that induce mainly perspective perception and objects principally inducing nonperspective stereoscopic perception; and generally to provide methods and means for testing the correct vision of eyes as determined by the comparative properties of orientation faculty, perspective and stereoscopic vision, respectively.

A further object of my invention is to detect and evaluate the presence of ocular image size and shape differences by comparing perspective and stereoscopic vision, to test eyes for the presence of imperfect space perception due to ocular image incongruences, including differences in declination, and to provide means for carrying out such investigations and eye examinations.

As broadly outlined above, my ocular testing method according to the present invention is based on the comparison of various types of space perception, namely vestibular orientation, monocular perspective vision, perspective stereoscopic vision and non-perspective stereoscopic vision.

Diiferent Ways of carrying out ocular tests based on such comparisons will now be described, whereby it is understood that various combinations and modifications of such methods are possible within the broad inventive concept of testing space perception by simultaneously effecting, and difierentiating between, various ways of bringing to consciousness the position of objects in space. It will also be understood that the herein given theoretical basis of the invention constitutes the best explanation of its practical aspects available to me at this time, but that changes in such theories as might be arrived at by further research will not materially change their practical embodiments herein disclosed and claimed.

For comparing non-perspective stereoscopic vision with the vestibular orientation faculty, an object inducing substantially only such vision is presented to both eyes, by excluding any factors that might induce perspective space perception, either monocular or stereoscopic.

For comparing non-perspective stereoscopic vision with monocular perspective vision, only one eye sees an object inducing perspective vision, whereas both eyes see a correlated object inducing only stereoscopic, but not perspective vision. In this case, ocular image discrepancies do not substantially affect space perception induced by the eye seeing perspectively, whereas they do aifect stereoscopic vision; hence they can be evaluated by comparing, in this case, the appearance of objects perceived with monocular perspective and non-perspective stereoscopic vision, respectively.

For comparing non-perspective stereoscopic vision with perspective stereoscopic vision, both eyes are presented with an object inducing only stereoscopic vision, and also with another object which induces perspective, preferably without being affected by ocular image incongruities. Eikonic defects can therefore be examined by comparing the apparent relative position of the two objects. Ways of practically carrying out this comparison will be described more in detail hereinafter.

My invention will first be explained with reference to Figs. 4 and 5 schematically illustrating In the field of view of the eyes is arranged an object adapted to induce non-perspective stereoscopic vision, for example, a plate or table T having a surface covered with an irregular pattern 10, preferably raised, or in relief, or otherwise adapted not to produce any effect of perspective that could induce perspective perception. A rough building board or a sheet with metal shavings glued thereto was found satisfactory for this purpose, but it will be understood that any object having the function herein discussed (namely that of a three dimensional pattern sufficiently irregular so as not to induce perspective space perception) can be substituted. Several embodiments of structures inducing only non-perspective stereoscopic vision will be described later with reference to Figs. 7, 8, 11, 12, 16, l7, 18, 21, 24 and 26.

Associated with table T is an object used primarily for inducing monocular perspective space perception. I found that a rectangular frame arranged as indicated at F serves this purpose. As especially shown in Fig. 5, table and frame are so dimensioned, and arranged with respect to the eyes, that the edges 1, 2, 3, 4 of the table are obstructed by frame F, so that the table does not present to the eyes any structure liable to induce perspective space perception.

For inducing perspective stereoscopic vision, three-dimensional rectilinear forms with disappearing lines are especially effective, as for example wires f, of Figs. 4 and 5. Other structures for the same purpose will be described hereinafter.

In certain instances, the configuration of the perspective structure is of no particular consequence. In that case, both eyes may see frame F and a wire structure 6, f, of Fig. 4-. Eikonic defects can then be detected and evaluated by moving table T relative to structures F, c, 1', since moving the table changes the stereoscopic perception thereof, but not that of the structure F, e, f.

In other instances, however, especially if test lenses changing the ocular image relation are to be used, it must be considered that any change of that relation, generally speaking, also affects perspective stereoscopic vision. Hence, in such cases care must be taken to avoid any influence of eikonic changes upon the object of comparison, the perspective object. Two ways of accomplishing this result will be described by way of example, as follows:

If the lenses are to be applied in such a manner that they cover both types of objects, perspective objects must be used that have no lines or forms which are influenced by relative changes of the ocular images. Such objects are, generally speaking, structures which do not have two objects laterally displaced so that their relative separation as seen by each eye could be judged. The wire structure shown in Fig. 27 meets this condition. It consists of a cross 225 225 normal to the line of vision, whose ends extend beyond the field of. view, with a third member placed in the line of vision of the cyclopean eye. This structure must be viewed through diaphragms, for example circular, that prevent the eyes from seeing any other lines or objects whose lateral position can be compared with line a.

If the eikonic lenses are applied in such a inanner that they cover only the non-perspective stereoscopic object, that is where they can not affect the stereoscopic appearance of a perspective object, the latter may in certain instances have lines and forms that are subject to change of appearance with change of eikonic relations. An arrangement of this type is indicated in 5, where lens D does not interfere with the visibility of structure e, f, as indicated by rays m, n. In this case, the eyes need not be masked, but of course the edges of table T must be hidden, for example, by frame F, in order to render the table a purely stereoscopic test object. The purpose and use of lens arrangements of this type will be described more in detail later.

It will be observed in this connection that the above discussed problem of avoiding the effect of eikonic changes upon a perspective object is not present in the case where monocular perspective is used for comparison with non-perspective stereoscopic vision, since, as above discussed, monocular vision is not substantially affected by eikonic changes; at least any influence of such changes upon monocular vision is of secondary order as compared with their influence upon nonperspective stereoscopic vision.

Instead of being arranged comparatively close to table T, frame F or several frames may be arranged nearer to the eyes, as for example approximately half way between table and eyes. In this case, the surface T will appear somewhat similar to a wall observed through several door frames looking down a hallway.

In order to relate non-perspective stereoscopic vision and vestibular orientation, all objects inducing perspective must be excluded, as explained before. For this purpose, screens MO may be placed in front of each eye, which screens, as indicated in Fig. 5 obstruct frame F to both eyes, so that nothing but non-perspective stereoscopic vision is present.

For comparing non-perspective stereoscopic vision with monocular perspective vision, the following structures are used. In order to induce monocular perspective vision of frame F, means are employed to obstruct to one eye the entire frame F, so that only the other eye can receive the impression of perspective. As indicated in Fig. 4, the left eye L can see everything within the sector indicated by lines a, b, c, d, whereas the right eye R can perceive objects within sector b, c, d (Fig. 5), in the present instance only table T. This effect can, for example, be accomplished by placing in front of the right eye a rectangular mask MR (Fig. 5) whose aperture sides are defined by rays ct, b, 0, (Z, and in front the left eye a mask ML similarly defined by rays a, b, c, d.

In most practical embodiments of this phase of my invention, it is not necessary to present to one of the eyes only the test object inducing monocular perspective vision, to the exclusion of objects not part of the testing apparatus. It is then not necessary to limit the vision of the eye (here the right eye R.) perceiving the test object (here frame F) so that mask MR, or equivalent means, can be omitted and the eye permitted to see the environment of the test set-up which, generally speaking, will likewise induce monocular perspective space perception.

For comparing perspective and non-perspective stereoscopic vision by excluding the influence of eikonic changes upon the perspective objects, both eyes are screened, for example with ma MB, from seeing frame F, so that, above d cussed, they see, respectively, only table T inducing stereoscopic vision, and a structure, inducing binocular perspective not influenced by eikonic changes.

As indicated in Figs. 4 and 5, both frame F and table T may be arranged for universal rotatory adjustment about axes A, B, and A, B, respectively, so that they can be moved into any desired position, preferably by the person being exai: ined. In most instances, it is not necessary to change the position of frame F, so that it may be fixed and only table T fitted with adjusting means.

Specific examples of such adjusting m ans will be given hereinafter, but care should be taken in every case where the patient himself operates them, that the instrumentalities for moving the test objects do not convey any indication of the position of the latter through judgment based upon sensory cues derived from such instrumentalities.

The position of the test objects at any time can e indicated, for example, by scales shown at AT, AF, BT and BF of Fig. 4, with appropriate indicators.

The first-mentioned test of comparing nonperspective stereoscopic vision with the vestibular orientation faculty is, for example, very valuable for examining the sight of aviators, and if so applied, the test should duplicate as nearly as possible the conditions under which a pilots eyes are used when flying, particularly when landing. The test is preferably made with a horizontal table which can be tipped to any angle. The person to be tested looks down on the table at the average angle of observation of a landing field. The table, for example irregularly marked with metal shavings, is preferably at a distance of about to feet. As mentioned before, both eyes are screened so that they see only the table and no object whatever that could induce perspective vision. It will be understood that, if only this type of test is to be performed, there is no need of using frame F and wire structure e, J, and that only table T, in combination with a head support (for example as described hereinafter) and a mask MB for each eye are necessary.

The aviator is so positioned that the masks present only the table surface, without its edges, and by suitable means (such as described hereinafter) he sets the table in a position that appears level to him. If his stereoscopic vision is good, the table as set will be actually level; if not, the table will be set at angles which indicate the persons defects in a manner which will be discussed hereinafter in connection with other modifications of my test which, however, are in this respect similar to the one noW discussed.

The above test is based on the assumption that vestibular orientation is substantially correct, and it is therefore desirable to check or test whether or not this is actually the case. Ac-

, cording to my invention, a test for that purpose can be carried out in the following manner.

In addition to being subjected to the above described test involving comparison between vestibular orientation and nonperspective stereoscopic vision, the person in question is also put through a test during which monocular perspective vision and non-perspective stereoscopic vision are compared.

I found that space perception induced by mo nocular perspective is least influenced by uncontrollable factors and can therefore be used as a standard. Hence, although vestibular orientation and monocular perspective can not be directly compared, by relating non-perspective stereoscopic vision to both vestibular orientation and monocular perspective vision (this test will be described in detail hereinafter), the former can be indirectly related to the latter, and in this manner checked against a substantially fixed standard. If the results of both tests are in agreement, it can be assumed with practically sufficient certainty that vestibular orientation is correct. Any difference between the results of these two tests indicates defective vestibular orientation.

Coming now to the comparison of non-perspective stereoscopic vision with monocularly' perspective vision, effected by table '1, frame F (structure e, 1, being removed) and masks ML and, if desired, MR, it will now be evident that a person whose eyes are located at L and R and masked by MR and ML sees table T with both eyes, neither eye being able to see the boundaries of the table.

Therefore, the table produces substantially only non-perspective stereoscopic space perception induced by its pattern, as for example a rough surface or one of the structures to be described hereinafter. The frame F can be seen with one eye only, here with the left eye. Hence, the position of the table surface will be known to the observer mainly through his non-perspective stereoscopic faculty, whereas the frame position is determined principally through the perspective of its image as received in one eye.

Any non-conformity in the nature of the two types of vision is made evident by a non-conformity in the position of the object for non-perspective stereoscopic space perception (here the table T) as compared with the position of the object conveying monocularly perspective space perception (here the frame F appearing in rectilinear perspective) Therefore, if the person examined suffers from non-conformity of monocular and stereoscopic vision and looks at a structure exemplified by Figs. 4 and 5, with the planes of frame and table set parallel, he will not see these two structures as parallel, but obliquely to one another. If now, by some means, the patient relatively moves the two structures until they appear to him parallel, his visual defect can be determined from the deviation from actual parallelism of the structures, which can be measured, for example, by means of the above described scales indicated in Fig. 4. Or, the visual defects can be determined by placing test elements, indicated at E of Fig. 5, before the eyes which cause the objects to appear in correct position. The test elements then indicate not only the nature of the defect but also its amount, and can be used directly to determine the design of spectacles for correcting the defects. Assum ing correct or corrected monocular vision, such lenses (whose structure and specific mode of operation is not a subject matter of the present disclosure) will consist of elements changing the relation of size or shape (including declination and distortion as above discussed), or both, of the ocular images, alone or in combination with one another or with power elements.

Although, as already discussed, defects of nonperspective stereoscopic vision caused by incongruous ocular images are the principal cause of incorrect space perception generally, and although, in the specific embodiments to be described below, only the object inducing non-perspective stereoscopic vision is shown adjustable and the object inducing another type of space perception and serving as a standard for comparison, remains fixed so that visual separation thereof from the environment is not necessary, the relative adjustment of the two types of objects may be performed in any other manner. Accordingly, both objects F and T are shown movable in Fig. 4. If the object for monocular perception (for example F) is to be adjusted, it is preferably disassociated from the environment. Thus, Fig. 5 shows a mask MR which performs this function.

In order to carry out the third above-discussed modification of my invention, namely the comparison of non-perspective stereoscopic and perspective stereoscopic vision, the outlines of the table (or whatever structure is used to induce nonperspective stereoscopic vision) are preferably screened from both eyes, although this is not necessary in all instances. Masks similar to MB of Fig. 5 may be used for this purpose, and frame F may be removed. The object inducing only binocularly perspective vision, as for example wires e, ,f, of Figs. 4 and 5, must be so arranged and supported that any structure associated therewith that might induce stereoscopic vision can be screened from both eyes. Various ways of accomplishing this result will be described hereinafter.

Again, as in the example dealing with the comparison of non-perspective stereoscopic and monocularly perspective vision, the two test objects are actually moved relatively to each other by mechanical means, or apparently by means of suitable optical elements, as prisms or size lenses, until they assume a desired apparent relative position. It is, generally speaking, preferable to adjust the position of the non-perspective stereoscopic test object and to retain the object of comparison fixed.

In evaluating ocular defects by means of corrective lenses, it is preferable to use such lenses before the eye which is not used for monocular perspective vision, in order to eliminate any possibility of secondary influences of an ocular image change upon monocular perspective.

While the comparison of stereoscopic vision with three other types of space perception has been discussed separately, it will be understood that these test modifications can be combined in various ways.

As mentioned above, various means for inducing stereoscopic vision may be used, an irregularly rough surface, as for example, metal shavings glued to a board being satisfactory in many instances. However, for certain tests it is desirable to use stereoscopic test objects which can be related to certain physiological facts which will now be shortly described.

As well known in physiological optics, the horopter is the surface in space every point of which is imaged on corresponding retinal points, whereby retinal includes the above-mentioned corresponding elements of retina and brain which are associated through nerve connections. However, due to the so-called fusion areas, a pair of eyes, fixed at a certain point is able to fuse objects within a certain space outside the horopter.

Expressing this condition in terms of horopter theory, it can be said that the horopter is surrounded by a spatial region of single vision, or, referring now to Fig. 6 (where R and L are the two eyes, respectively, It the longitudinal horopter in the visual plane, FP a fixation point, tm the trace of the median plane and if the trace of the fixation frontal plane on the plane which includes the visual axes), that the longitudinal horopter h is flanked by two lines he and hi enclosing an area of single binocular vision or fusion.

It will now be apparent that a three-dimensional pattern to be used for inducing stereoscopic vision should on the one hand lie well within the fusional area, but also, on the other hand, should sufficiently extend in the direction of the line of vision to induce space perception. In Fig. 6 the area of such a pattern, assumed to be limited by plane surfaces, is indicated at r and 8. Since the fusional area varies considerably with different individuals, I use, according to my invention, stereoscopic test patterns which can be adjusted to conform to the fusional area of different individuals. For example, referring now to Fig. 7, irregular patterns, as spots of paint 0, may be applied to glass plates 20 and 30 which are mounted parallel and whose distance can be adjusted by suitable means, an embodiment of which will be described hereinafter. Or (Fig. 8), a two-dimensional pattern may be applied to a transparent medium and rendered three-dimensional with the aid of a mirror 42! producing a virtual image of pattern 0' at 0. Object O and image 0" together represent a three-dimensional pattern whose extent in the direction tm (Fig. 6) can be adjusted by changing the distance between object O and mirror 49.

Certain ocular image differences, mainly those of an asymmetrical order which can be reproduced by prism effects, cause the stereoscopic vision objects, for example, table T to appear warped. According to one aspect of my invention, I examine and evaluate this eifect by warping the table to compensate for this defect, the amount of warping necessary being a measure of the defect.

For this purpose, the table may be arranged as shown in Figs. 9 and 10. In these figures, 9 represents a rigid plate, for example supported on a ball and socket joint and stand 1. Attached to rigid plate 9 is a flexible table 8, by means of spacers of adjustable length connecting a number of corresponding points of plate and table. Any suitable means for adjusting the spacers may be used, Figs. 9 and 10 showing screws 9 attached to the table with ball joints and turning in nuts i fastened to plate :3. By means of flexible shafts l2 and hand knobs 13, the lengths of the respective spacers can be adjusted, and their amounts read by means of scales 14. By mounting knobs !3 on a board [5 (Fig. near to the observers position, and by distributing them similar to the spacers, the arrangement of the testing table can be reproduced on a smaller scale. It will now be apparent that by applying a suitable number of adjustable spacers, table 8 can be warped into any shape, and the configuration of the warped surface measured, and hence also the nature of an eye defect which causes a plane surface to appear warped and which can be compensated by actually warping the surface.

It is understood that other means, suitable for the peculiar arrangement required, can be used for adjusting the test table surface.

Although arrangements similar to Figs. 4 and 5 permit the carrying out of my new testing method with respect to deviations in all three dimensions, and are particularly applicable to investigations of binocular vision in reading position (to be described more in detail hereinafter), I found it in many cases more desirable to separate the tests for the two main object planes, namely the horizontal plane and a vertical plane substantially perpendicular to the line of vision. This separation not only permits more exact determination of the correlation of ocular defects and corresponding object appearances, but it also simplifies tests in cases where objects appearing mainly on. a certain plane are of principal importance.

An instrument especially suited for investigating the perception of objects mainly in a horizontal plane, or deviations about horizontal axes, will first be described with reference to Figs. 11 to 15.

Instruments of this type are especially valuable ior testing aviators for their stereoscopic vision, either by comparison thereof with the vestibular orientation faculty, as above explained, or any other method according to my invention. They duplicate in essence the conditions under ill) which pilots use their eyes when flying, particularly during landing. The general arrangement is so that the aviator looks down on an approximately horizontal test table at the average angle of observation of the ground when landing. The table is preferably placed at a comparatively great distance, for example to feet, although shorter distances may be used.

As shown. in Figs. 11, 12 and 13, a stand I6 is provided (which may be placed on a raised platform in order to obtain the proper angle of observation) carrying eye positioning means IT, for example of the type described in copending application Serial No. 706,523, filed January 13, 1934, or of any other suitable construction. In the present embodiment, a slotted bracket l8 supports an arm I9, which can be laterally adjusted, for example by means of screw 2|. Clamped to a slotted sleeve of arm I9 is a column 22 which supports at its upper end a chin rest 23 and a forehead support 24. As shown in Fig. 12, support 24, after loosening screw 25, can be rotated about column 22 and also adjusted vertically. Extension 26 and screw 2'1 permit a tilting of support 24. With a nut 28 the threaded and slotted spindle Z9, and with it chin support 23, can be raised and lowered.

It will be understood that by this, or similar means, the head of a patient can be fixed relatively to the testing means and that by using appropriate scales, as for example described in the above-mentioned copending application, any head position can be reproduced for future tests.

Also supported by column 18 is an optical head 3|. This structure can be tilted by means of a joint 32 and fixed in any desirable position by tightening screw 33. Extension 34 slides within column I6 and can be fixed thereto at any height and. angular position with screw 35. The head 3| proper has a base 4| on which are mounted corneal sights G2 which are merely schematically indicated in Fig. 12 and may be of any desirable type, for example as described in the above-mentioned copending application. Lens holders 43 are fastened to base Al as shown more in detail in Figs. 14 and 15. One holder is provided for each eye and each preferably slides on the base independently of the other with dovetail keys M. Screws 45 rot'atably fastened in rim 48 of base 6| (Fig. 14) and engaging a thread in key 44, serve for adjusting the lens holders to the pupillary distance of each individual patient. Mask holders 4! are similarly fastened to base 4| and adjustable with screw 48 (Fig. 12). The lens holders have grooves 69 for receiving trial lenses in a. well-known manner. Provisions for continuously adjusting the image size, according to copending application Serial No. 713,701, filed March 3, 1934, may be added.

It will be evident that any suitable construction can be employed for adjusting optical head and lens holders and that indicators and scales can be associated with these structural elements in order to measure and reproduce their various adjustments.

A separating wall or septum 5| is arranged approximately midway between the eyes. As shown in Fig. 12, septum 5| has a cutout which permits both eyes to see both sides of the table. but not of the frame. A septum insert 5| may be slidably fastened to 5| so that edge 5| can be moved in accordance with changing conditions of eye position and test objects. Screens or masks 52 are provided between respective eyes and test objects. These screens can be adjusted for proper pupillary distance and may be removable and interchangeable for screens of different apertures, for carrying out different phases of the test herein described. For example, there may be one screen in front of one eye only, corresponding to mask ML of Fig. 5, or one of two screens with two apertures functioning as indicated at MO, 1M1 and ML of Fig. 5. These screens or masks may be mounted adjustably and with indicators and scales, in a manner needing no further explanation.

At a suitable distance from optical head 3| is arranged a frame support 88 having, for example, four post's 8|, 62, 63, 64 (Fig. 11) supporting a frame 65 corresponding to, and dimensioned according to element F of Figs. 4 and 5. A frame structure H having two trunnions i2 is journaled in uprights 13, M or similar supports. Frame H supports table 15 having two shaft portions 18, 11 extending into frame 1| in which they are journaled. Table '75 corresponds to element T of Figs. 4 and 5 and, as explained with reference to these figures, has applied to its surface a three dimensional pattern, indicated as shavings 18. For moving table 15, the following arrangement is provided. A drum 8| (Fig. 11) with hand wheel 82 is journaled on stand l6. Ropes or chains 83, 8d are fastened to the drum and guided over rollers 85 (Fig. 12) toward frame ii to which they are suitably fastened. A similar, in this instance smaller, drum 88 with hand wheel 81 is journaled on stand it perpendicular to drum 8|. A rope 88. is wound around drum 88 and, over guide rollers 89, conducted towards table 15 to which its ends are fastened. It will be evident that operation of hand wheel 82 swings table 15 about trunnions 12, whereas operation of hand wheel 81 rotates the table about shafts l6, '11. Hence, the table can be brought into any possible inclined position. Hand wheels 82 and 8? being arranged at an angle, and drums 8| and 88 being of different diameters, the patient setting the table can not in any way connect the amount of travel of the hand wheels with the amount of displacement of the test object, which is important for reasons discussed above. Instead of supporting the table as above described, it may be mounted on a ball socket approximately at its center, with moving means, as ropes, or rods, attached directly to the table.

In order to measure the position of the table, trunnion 'i'i has an indicator 9! playing on a scale 92 fastened to frame H (Fig. 13). Similarly a pointer 93 is fastened to frame H and associated with scale 94 connected with frame structures 85, for example fastened to post 82 (Fig. 12). With the aid of these two pairs of scales and pointers, the position of table '15 can be accurately determined. If desired, the scales can be calibrated directy to indicate eye defects involved in per cents of size defects, and, for declinations (this concept will be explained hereinafter), in inclinations of the axis of a cylindrical size lens correcting the declination.

In order exactly to determine the spatial rela- 1 tion of the eyes to be tested and the testing objects, stand it and posts 5| to 8 1 may be fastened to the ground in predetermined positions (Fig. 11) or they may be correlated by suitable adjusting members, as for example trucks running on common rails with scales or similar means suitable for adjustably but positively relating the positions of eyes and test objects (not shown).

Apparatus for testing the perception of objects preponderably in :a vertical plane, or the vertical aspect of space perception, is shown in Figs. 16 and 17. In these figures, IIlI is a base supporting aframe structure I02 and a turntable I03. Pivotally supported in frame IE2 is screen I04. Fixed to the ground, or to base IllI, is a frame IE5. It will be understood that screen IE4 and frame 65 correspond to elements T and F, respectively, of Figs. 4 and 5, and are to be arranged and dimensioned in accordance with the principles discussed in connection with these figures. Suitable means for adjusting screen i534, and for measuring such adjustments, should be provided. For example, the ropes shown in Fig. 11 as controlled by hand wheels 82 and 81 can be connected to the vertical testing apparatus as shown in Figs. 16 and 1'7. In these figures ropes 83 and Be are fastened to top and bottom of screen I84, whereas rope 88 is slung around the upper disk of turntable 33. It is evident that this arrangement permits universal adjustment of screen N34. The movements of the screen can be determined by scales III and IE2 on upper turntable disk and frame I62, respectively, which are associated with indicators I53 and H4 on the lower turntable disk and the pivot of screen I84, respectively.

Again, optical head SI (Fig, 12) and test objects can be interrelated in space by fastening them to the ground, or by means for positively and measurably moving these two units relatively to each other.

If the latter embodiment is used, for example by mounting the test objects on rails, the set up can be so arranged that the two types of objects can be interchangeably used with the same head support and optical head, by positively and reproducibly positioning each object relatively to the eyes to be tested. In this manner, it is possible to correlate in a single test what may be called the horizontal and vertical aspects of space perception.

t will be understood that a test object structure according to Figs. 4 and 5, that is one having no special position in space, will be used in combination with head support and optical means shown in Fig. 12. In this case, both frame F and table T are mounted on means functioning, for example, similar to those shown in Figs. 11 and 12. Both adjusting and measuring means for frame F are quite similar to those of table 'I, as will now be understood without further explanation.

With apparatus of this type, that is with both objects (that for stereoscopic and that for perspective space perception) universally adjustable, investigations of the interrelations of space perception due to the faculty of vestibular orientation, monocular perspective, and perspective and non-perspective stereoscopic vision, and of the characteristics and defects of each type of perception, can be carried out in a quite comprehensive-r manner.

While the above-described embodiments can be adapted for performing ocular examinations at any desirable visual distance, I found devices similar to that now to be described suitable for performing tests at near distance and especially for reproducing conditions during reading, for purposes where no particular exactitude of measurements is required. Figs. 18 and 19 show a device of this type which may either be held in the hands of the patient like a book, or supported on a stand, table or other suitable structure. It has a box-like body portion l2i with a rectangular opening Hii in its upper Wall which is preferably covered with the marginal portion of a sheet of printed matter, or a picture, or other object i222 adapted to induce perspective space perception and at the same time simulating matter that is usually viewed at near distance. Within the box is adjustably mounted a sheet I23 of material having an irregularly rough surface inducing stereoscopic space perception. Any suitable device, as universal suspensions similar to those shown in Figs. 11 and 12 in connection with screws, racks and pinions, etc., may be used for adjusting the relative position of sheet I23 and box surface i252. In Fig. 19, sheet I22 is supported by a swivel stick I24 with a ball shaped portion 525 sitting in perforated socket I25 of the box, against which it is frictionally pressed by a rubber or other elastic plate 121. By appropriately moving handle I28 of the stick, sheet 523 can be moved in any desired relation to the box. Scales for measuring the adjustment in any direction can be added in a manner similar to that shown in Figs. 11 to 13 or in any other suitable way.

The protruding length of handle I28 may be made adjustable, for example, by using a sliding handle fastened to stick I24 with screw I29. By changing the leverage of the handle, visional and other means of space perception can be disassociated. In addition, handle I28 may be bent, for the same purpose. A device of this type may either be used in connection with a head positioning means as shown in Fig. 12, or without such arrangements. In the latter case, the patient is fitted with masking spectacles or similar means, as shown in Fig. 20. This figure shows a conventional trial frame MI fitted before one eye with a mask I42 having a rectangular aperture ginal portion I22 of box I2I from the respective eye which, in this manner, contributes only to non-perspective stereoscopic space perception, whereas the other eye sees also the characteristics space perception. The box is so placed on a support, or the patient instructed to hold it in such a manner, that its relation to the eyes corresponds to that shown in Figs. 2 and 3, which needs no further explanation.

Assuming that frame I22 and plate I23 are initially set parallel, if the patients space perception is imperfect, he reports that they are inclined relatively to each other; he can then be instructed to move handle I28 until both objects are parallel, whereupon the defect can be evaluated with the aid of indicators or scales. Or, suitable optical test corrections can be placed in frame I4I as indicated at I45 and I46.

As pointed out before, correct space perception can be established, and the defects measured, by placing before the eyes test corrections comprising, for example, size changing lens elements according to Patent No. 1,933,578, but preferably adjustable eikonic lens units according to copending application Serial No. 713,701, filed March 2, 1934. Such elements are not necessarily performing functions substantially equivalent t0 the mechanical adjustment of the test objects, but rather eliminate the ocular image defects, which constitute the cause of the'elfects demonstrated according to the new testing methods.

An instrument embodying most previously discussed features, and primarily intended for near tests but easily adaptable for distant tests, is shown in Figs. 21 to 29.

This instrument, in the modification shown, has a base I58 to be set upon a table or fixed to 35 I43 which is so proportioned that it screens mar .40 of frame i22 which induce monocular perspective a suitable support, and a front piece I5I for mounting head rest, test supports and masks. In order to simplify the drawings, only a chin rest I52 (Fig. 22) is shown, but it is understood that a universally and reproducibly adjustable head support as previously described will be used in most cases. Also for the sake of simplicity, only a comparatively simple lens and mask holding arrangement is shown. It comprises two brackets I53, I53 drilled for four rods I54 to I51 with suitable handles I58 moving therein with some friction so that they remain in any position in which they are set.

Fastened to rods I54 and I56 are trial lens holders I 6| and I62, each, for example, accommodating two trial lenses. Rods I55 and I51 support mask holders I63 and I64 to which masks I65 and I66 are fastened. By adjusting rods I54to I51 in their brackets, lens holders and masks can be adjusted to fit the pupillary distance of the eyes. By rotating rods I55 and I51, any one or both masks can be removed from the field of vision, as for example, in Figs. 21 and 22. It will be understood that more elaborate and exact lens and mask supporting means can be used, and especially that adjustable size lens units according to the abovementioned copending application, Serial No. 713,- 701, can be mounted. Also, means for aligning the eyes, including cornea sights, as shown in copending application Serial No. 706,523 will be used in most instances in connection with the head-positioning means.

A slanting board I1I has a slot I12 for a screw I13 with thumb nut I13 adjustably holding in place flange I14 of frame F. In order to induce perspective space perception, window I16 of frame F may be surrounded by a molding I16 (Fig. 23). An exchangeable paper mask I11 may be used for adjusting the size of the window.

Rotatably fastened to board I1I, as by means of a pin I8I, is a U-shaped (Fig. 24) support I82 for test screen T, which swings in support I82 by means of screws I83, I84, which also permit fixation of the screen at any inclination relatively to the U support. It will be apparent that by means of pivot I8I and screws I83, I84, screen T can be rotated about two axes and hence brought into any possible angular relation tothe line of vision. Means suitable for conveniently moving screen T about those two axes may be added, as for example, hand wheels and ropes attached to the screen and running over pulleys to the hand wheels. The position of screen T can be determined with the aid of two circular scales I86, I81, fastened to board HI and screen T, respectively, and two pointers I88, I89 on support I82.

The screen is of the adjustable type explained above with reference to Figs. 6 to 8, and comprises two frames NH and I92 holding glass plates I93 and I94, respectively, with a pattern applied to their surfaces. The two frames are spaced by four pins I95 fastened to frame I 9! and movable in bushings of frame I92, for example, by means of rack and pinion drives shown in Figs. 21 and 25, and permitting easy adjustment of the plate distance by turning knob I99.

The screen is illuminated from behind by means of a lamp arrangement comprising a board 2Ill, a reflector 262 and a lamp 263. In the instrument shown, the rear plate I94 is an opal plate having a pattern on the inner surface, whereas plate I93 is transparent and has a similar pattern, likewise on the inner surface. Instead, two transparent plates and a diffusing surface covering reflector 282 could be used.

For carrying out tests with correlation of binocular perspective and stereoscopic vision, a perspective structure may be applied as follows, although frame F (Figs. 4 to 21) alone is often suificient for that purpose.

Referring now especially to Figs. 26 to 28, a box-like frame 2H is mounted on board 2I2 which can be put against frame F, with the portion 2I4 of the box extending into the frame window. Within the box are four sheets 22I, 222, 223, 224, forming a perspective structure which, if desired, can be supplemented by a wire frame 225 which constitutes the above described perspective structure which is not influenced by relative changes of the ocular images.

For making tests with lenses affecting the ocular image relation and not covering the perspective pattern, the following, or similar provisions, may be made, referring now especially to Figs. 26 and 29.

A standard 23I is adjustably fastened to board I1I, for example, with a screw clamp 232 permitting adjustment of the standard in the plane of board I1I by changing the position of clamp base 24I, as well as perpendicularly thereto by means of a rack and pinion arrangement 242. A boss 233 of standard 23I rotatably supports rod 234 which has a similar boss 235 holding rod 236 for lens holder 231. Knobs 238, 239 permit rotation of lens I in lens holder 231 about two perpendicular axes intersecting at its center.

By way of example, some effects of aniseikonia as evaluated with the aid of my new testing method will now be described. If meridional aniseikonia is present in the form where the ocular images are different in the horizontal meridian, the two ocular images are related as diagrammatically indicated in Fig. 30. In this figure, it is assumed that the ocular image IL of the left eye is an undistorted reproduction of an object field represented by a square, whereas the ocular image IR of the right eye has greater horizontal dimensions than IL. I found that to a patient having this defect, the two test objects of apparatus according to Figs. 2 and 3 seen with perspective (either monocular or binocular) and non-perspective stereoscopic vision, respectively appear laterally inclined as shown in Fig. 31, where FH and T indicate the actual normal positions of frame and table, respectively, whereas TI indicates the apparent position of table T. Fig. 31 is a front view of the table T in Fig. 12 seen in the general direction of the patients line of vision, as indicated by the axes which are marked A and B like the corresponding axes of Figs. 4 and 5. If the patient adjusts the table until it appears to him horizontal and parallel to frame FH, it will assume position T2.

Figs. 32 and 33 indicate similarly the effect of aniseikonia in the vertical meridian, where the vertical dimensions of ocular image IR are greater than those of the other ocular image IL. Fig. 33 is a top view of the vertical testing screen.

Theoretically, an image difference of this type should have no effect on stereoscopic space interpretation, because the disparity is not in the direction of the separation of the eyes. It was found, however, that an artificially produced increase in the vertical meridian of one eye does effect the apparent lateral tipping. The amount of this effect on observers who have no vertical size difference is as if the horizontal meridian of the other eye were increased by about half of the vertical size change in the first eye provided the test is made with the horizontal tilting table 

